Lieutenant General Sergei Sevryukov blamed mobile phone use by its soldiers for the incident.
"At the present time, a commission is working to investigate the circumstances of the incident. But it is already obvious that the main reason for what happened was the switching on and mass use by personnel - contrary to the ban in place - of mobile phones in a strike zone accessible to enemy weapons. This factor allowed the enemy to track and determine the coordinates of the soldiers' location for a missile strike."
The New Year's Eve strike in Makiivka is the deadliest single incident Moscow has acknowledged since the start of the war.
The defense ministry said four Ukrainian rockets hit a temporary Russian barracks in a vocational college in the Russian-occupied Donetsk region in eastern Ukraine.
Ukraine initially said hundreds of Russians were killed. It has since avoided giving details.
The attack has angered pro-war Russian commentators, who are increasingly vocal about what they see as a half-hearted and incompetent campaign in Ukraine.
Criticism has been directed at military commanders rather than Russian President Vladimir Putin.
He has not commented publicly on the attack, which has dealt a further blow after major battlefield retreats in recent months.
Russia has effectively shut down all direct opposition to the war, with open criticism banned by severe media rules.
But it has given comparatively free rein to pro-war nationalist bloggers, many with hundreds of thousands of followers on social media.
Ukrainian President Volodymyr Zelenskiy, who rarely comments on specific Ukrainian military strikes, made no mention of the attack in a video address on Tuesday.
He instead said that Russia was set to launch a major offensive.
Kyiv has been saying for weeks that Russia plans to order another mass conscription drive.
In the latest sign that the Kremlin may be considering such a move, a little known group claiming to represent widows of Russian soldiers released a call for Putin to order a large-scale mobilization of millions of men.
Putin said last month that there was no need for an additional mobilization after he ordered what he cast as a "partial mobilization" on September 21.
